Expression and biological significance of Ca 2+ ‐activated ion channels in human keratinocytes

In whole‐cell recordings from HaCaT keratinocytes, ATP, bradykinin, and histamine caused a biphasic change of the membrane potential consisting of an initial transient depolarization, followed by a pronounced and long‐lasting hyperpolarization. Flash photolysis of caged IP 3 mimicked the agonist‐induced voltage response, suggesting that intracellular Ca 2+ release and subsequent opening of Ca 2+ ‐activated ion channels serve as the common transduction mechanism. In contrast, cAMP‐ and PKC‐dependent pathways were not involved in the electrophysiological effects of the extracellular signaling molecules. The depolarization was predominantly mediated by a DIDS‐ and niflumic acid‐sensitive Cl − current, whereas a charybdotoxin‐ and clotrimazole‐sensitive K + current underlay the prominent hyperpolarization. Consistent with the electrophysiological data, RT‐PCR showed that HaCaT keratinocytes express two types of Ca 2+ ‐activated Cl − channels, CaCC2 and CaCC3 (CLCA2), as well as the Ca 2+ ‐activated K + channel hSK4. That the pronounced hSK4‐mediated hyperpolarization bears significance on the growth and differentiation properties of keratinocytes is suggested by RNase protection assays showing that hSK4 mRNA expression is strongly down‐regulated under conditions that allow keratinocyte differentiation. hSK4 might thus play a role in linking changes in membrane potential to the biological fate of keratinocytes.—Koegel, H., Alzheimer, C. Expression and biological significance of Ca 2+ ‐activated ion channels in human keratinocytes. FASEB J. 15, 145–154 (2001)